1. Field of the Invention
The present invention relates to a composition for use in compression refrigeration and to a lubrication method using the composition. More particularly, the present invention relates to a composition for use in compression refrigeration making use of a refrigerant containing a C1-C8 hydrocarbon, and to a lubrication method using the composition.
2. Description of the Related Art
A refrigeration cycle of a refrigerator such as a compression-type refrigerator including a compressor, a condenser, an expansion valve, and an evaporator is generally designed such that a liquid mixture of a refrigerant and a lubrication base oil circulates in the closed system. In such a compression-type refrigerator, dichlorodifluoromethane (R-12) and chlorodifluoromethane (R-22) have conventionally been employed as a refrigerant in many cases, and a variety of mineral oils and synthetic oils have also been used as a lubrication base oil. However, chlorofluorocarbons such as R-12 and R-22 involve the risk of inviting environmental pollution such as destruction of the ozone layer existing in the stratosphere. Therefore, use of chlorocarbons has come to be more strictly restricted throughout the world. As substitutes therefore, hydrogen-containing fluoro-compounds such as hydrofluorocarbons and hydrochlorofluorocarbons have recently become of interest. Although the hydrogen-containing fluoro-compounds, particularly hydrofluorocarbons led by 1,1,1,2-tetrafluoroethane (R-134a), will not destroy the ozone layer, their long lives in the atmosphere invite some concern about possible contribution to the greenhouse effect. Therefore, a variety of hydrocarbons, inter alias, C1-C8 hydrocarbons, have now come to be studied, as they are free from such problems.
However, when a lubrication base oil prepared from a mineral oil or alkylbenzene--which are conventionally used quite commonly--is used in a compression-type refrigerator in which hydrocarbons are used as a refrigerant, the refrigerant completely dissolves in the lubrication base oil to reduce the viscosity of the lubrication base oil. As a result, lubrication performance becomes insufficient to reduce antiwear effects, or sealing materials incorporated in the circulation system for the refrigerant degrade to make the sealing effect poor, which may prevent consistent use of the refrigerator over a prolonged period. Particularly in the case in which a capillary tube serves as an expansion valve, there is a strong tendency of sealing effect becoming poor.